[1] Univ Calif San Diego, Dept Pediat, Div Emergency Med, Rady Childrens Hosp, San Diego, CA 92103 USA
[2] Univ Pittsburgh, Sch Med, Div Toxicol, Dept Emergency Med, Pittsburgh, PA USA
[3] Univ Penn, Sch Med, Dept Biostat & Epidemiol, Philadelphia, PA 19104 USA
[4] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Epidemiol, Epidemiol Data Ctr, Pittsburgh, PA USA